The invention concerns a method for the manufacture of gear roller crimped metal fibers and products comprising these fibers, e.g., in the form of metal fiber bundles. In addition, products derived therefrom such as blended yarns of textile and crimped metal fibers are described, as well as sintered and nonsintered metal fiber webs.
From the German utility model (Gebrauchsmuster) No. 7521192 of applicant, it is known to crimp metal fiber bundles by passing them between gear-wheels. However, in this process, the pressure on the bundle by the tooth tops during the crimping process causes the filament sections to plastically deform at the crimped tops, due to crushing. According to the relative position of the fibers in the bundle thickness however, this crimping operation will have a different crushing or flattening effect, and will consequently cause a certain arbitrariness to the continual and permanent character of the crimping along the bundle. Also, the bundle will often be strongly compacted in the area of the crimped tops, so that adjacent fibers could undesirably catch onto each other, which would render it difficult to separate them during later operations. This disadvantage could however be alleviated by opening the bundle laterally before it runs through the gear wheels. Besides the fact that this attempted solution requires an additional opening operation, it was found that such an opening operation will rarely give fully satisfactory results, i.e., realize a very durable crimping operation.
In order to avoid these disadvantages, this invention now proposes to avoid direct contact of the gear wheels with the fiber surface during the crimping operation. The method according to this invention for manufacturing a gear roller crimped metal fiber bundle with a permanent crimping wave deformation provides a practical solution to the above mentioned problems, by embedding the metal fiber bundle in a ductile and coherent matrix material, and subsequently passing this composite matrix/fiber bundle between the teeth of at least two intermeshing gear rollers, after which the matrix material is removed.
In accordance with the present invention, every fiber of the bundle should preferably be enveloped by the matrix material, so that each fiber will be separated from adjacent fibers. In this way, every single fiber in the bundle gets a permanent crimping deformation, without being touched by gear teeth or adjacent fibers. If the fibers in the composite are relatively straight and parallel to each other, this crimping deformation will be essentially identical in every fiber. Moreover, with this crimping deformation, the average fiber section form will remain the same for the whole length of the fiber. For certain purposes, it can be sufficient to apply a simple, almost sinusoidal zigzag crimping (in one plane) with a wave length W between 2 and 30 mm and a wave amplitude A between 0.2 and 7 mm with W/A&gt;2 and preferably W/A.gtoreq.4. This crimping can be applied by passing the bundled composites, arranged in parallel, through the nip of two gear wheels that adequately engage or intermesh with each other, and that have mutual parallel axes of rotation.
Of course, the bundles can be forwarded successively through the nip of two or more pairs of gear rollers with mutual parallel axes of rotation. The depth of engagement with a next pair of rollers and/or the circumferential breadth of the individual tooth surfaces of the next pair of rollers could then differ from the previous pair. In this way, the crimping degree can be increased in steps, and/or one or more zigzag deformations can be superposed on the first one, in order to realize a more or less irregular crimping wave. By an adequate adjustment of the rollers, if desired, a crimping wave with a predetermined degree of irregularity can be realized. The limits for W and A, applied with the help of several pairs of gear rollers, will preferably lay between the values indicated above, so long as W/A&gt;2. A dominating or base-crimping operation with zigzag form can be carried out with, e.g., 4 mm&lt;W&lt;20 mm or 4 mm&lt;W&lt;15 mm, and upon which then a second (and possibly a third) zigzag wave can be superposed with a smaller wave length.
Also, the composite matrix/fiber bundle can be passed through the nip of at least two cooperating pairs of gear rollers having axes of rotation that are nonparallel. This will also produce an irregular crimping wave, at least partly tri-dimensional as a result of the superposed zigzag deformations.
The metal fibers, e.g., stainles steel fibers, can have a diameter between 4 and 25 microns. The number of fibers in the composite bundle will preferably amount to no more than 2000, and will usually lie between 500 and 1500, in order to be able to realize an easy plastic crimping deformation, especially when the matrix material for the composite bundle is also a metal.